Parmotrema saxoisidiatum is a rare species of saxicolous (rock-dwelling), foliose lichen in the family Parmeliaceae.

The type specimen was collected from Floreana Island at an altitude of 365 m (1,198 ft), where it was found growing on a lava cliff.

[2] The upper thallus surface of Parmotrema saxoisidiatum is white to whitish gray, with a dull to shiny texture and densely reticulated and speckled appearance.

It is often isidiate, with cylindrical isidia that are mostly simple or sparsely branched, occasionally clustered and longer along the lobe margin.

The lobes are small to moderate-sized (typically 0.3–4 mm wide), angular, and have sparsely to abundantly ciliate margins.